The present invention relates to the field of semiconductor integrated circuits. The invention is illustrated in an example with regard to a semiconductor integrated circuit cleaning technique using a multi-tank cleaning apparatus, but it will be recognized that the invention has a wider range of applicability. Merely by way of example, the invention can also be applied to the manufacture of raw wafers, lead frames, medical devices, disks and heads, flat panel displays, microelectronic masks, and other applications requiring high purity wet processing such as steps of rinsing, cleaning, drying, and the like.
In the manufacture of semiconductor integrated circuits, the efficient use of the fabrication facility is important. In particular, fabrication facilities are a limited resource, which can cost hundreds of millions of U.S. dollars to build. Once the fabrication facility is built, it is often difficult to upgrade such facility for the purpose of adding more floor space or the like. Most commonly, another fabrication facility is built in order to add floor space for additional capacity or an additional process. The process of building these fabrication facilities is often time consuming, difficult, and costly.
Additionally, as devices become more complicated, equipment used for the manufacture of these devices also becomes further complicated. Typically, equipment used in the fabrication of wafers becomes more expensive with each new generation. In addition, as the complexity of this equipment increases, so does its size. This larger sized equipment often occupies a larger footprint on the fabrication floor facility, which is an expensive and a limited resource. The use of larger equipment increases the cost of using such equipment further.
Furthermore, as these devices become more complicated, wafers generally become larger. These larger wafers must use larger wafer boats. The larger wafer boats can often only be used in larger processing equipment. Larger processing equipment occupies a greater floor space in the fabrication facility. The larger sized equipment requires a larger facility, which further adds to the total cost of manufacturing an integrated circuit.
Semiconductor integrated circuit fabrication equipment which generally increased in size with each successive generation includes many commonly used rinsing and drying systems. In particular, a conventional spin rinse/dryer increased in size to accommodate larger wafers. That is, six inch wafers generally do not fit inside the chamber of a spin rinse/dryer apparatus designed for four inch wafers or the like.
In conventional existing fabrication facilities, the spin/rinse dryer must often be replaced frequently to maintain low particle counts and low equipment failure rates. In particular, the spin rinse/dryer has an extremely complex mechanical design with numerous moving parts. The complex mechanical design often leads to certain problems such as greater downtime, wafer breakage, more spare parts, greater costs, among others. A further limitation is static electricity often builds up on the wafers during the spin cycle, thereby attracting numerous particles onto the surface of the semiconductor.
Some tens of thousands spin/rinse dryers are being used in the conventional fabrication facilities world-wide. Most of these spin/rinse dryers should be replaced in the next few years. These spin/rinse dryers, however, generally occupy a relatively smaller footprint than other types of drying systems. This means that spin/rinse dryers are generally replaced by another conventional spin/rinse dryer, which would probably need replacement within a few years after being introduced into the fabrication facility. There are simply no good alternatives to replace these spin/rinse dryers. Accordingly, a variety of potential problems occur, even after introducing a new spin/rinse dryer, which still has a variety of limitations. U.S. application Ser. No. 08/555,634 describes many of these limitations.
Other techniques used to dry wafers include an isopropyl alcohol (IPA) vapor dryer, full displacement IPA dryer, and others. These IPA-type dryers often rely upon a large quantity of a solvent such as isopropyl alcohol and other volatile organic liquids to facilitate drying of the semiconductor wafer. An example of such a technique is described in U.S. Pat. No. 4,911,761, and its related applications, in the name of McConnell et al. and assigned to CFM Technologies, Inc. McConnell et al. generally describes the use of a superheated or saturated drying vapor as a drying fluid. This superheated or saturated drying vapor often requires the use of large quantities of a hot volatile organic material. The superheated or saturated drying vapor forms a thick organic vapor layer overlying the rinse water to displace (e.g., plug flow) such rinse water with the drying vapor. The thick organic vapor layer forms an azeotropic mixture with water, which will condense on wafer surfaces, and then evaporates to dry the wafer.
A limitation with this type of dryer is its use of the large solvent quantity, which is hot, highly flammable, and extremely hazardous to health and the environment. In fact, this dryer needs a "small chemical plant" including a vaporizer and a condenser to handle the large quantities of hot volatile organic material. This dryer including its small chemical plant is often massive in size and requires a large floor space in the fabrication facility. As wafer size increases, so does the size of the IPA dryer, which occupies even a larger floor space for handling larger wafers. Though not used as commonly as spin/rinse dryers, the IPA dryers cannot be used to replace the spin/rinse dryers due to their massive size. That is, an IPA dryer cannot be placed on the same floor space that was previously occupied by a conventional spin/rinse dryer.
Still other techniques such as the quick-dump, the cascade rinse, the hot deionized (DI) water process and the like also suffer from similar limitations. In addition, these techniques generally rely upon tanks, which are increased in size to hold larger wafers. These larger tanks often include more processing fluids, which must be replenished repeatedly. Larger tanks also occupy a larger floor space in the fabrication facility. These techniques also require separate rinse and drying stations, which occupy even more floor space. Additional limitations of these techniques are described in detail in U.S. Pat. No. 5,772,784, noted above.
A pioneering approach that was developed to effectively clean and dry semiconductor wafers is a motionless drying technique using ultra-clean fluids described in U.S. Pat. No. 5,571,377 in the names of Mohindra, et al. and assigned to the present assignee, YieldUP International. This technique generally cleans and dries semiconductor wafers using ultra-clean fluids in an apparatus which allows the wafer to be substantially motionless during processing. It would be desirable, however, to provide this technique using a smaller footprint and higher capacity for processing large runs of integrated circuits and the like.
From the above, it is seen that a cleaning method and apparatus for semiconductor integrated circuits that is safe, easy, reliable, and occupies a relatively small footprint is often desired.